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KVM Virtualization Performance With Linux 2.6.31

Phoronix: KVM Virtualization Performance With Linux 2.6.31

Earlier this month at the Red Hat Summit where Red Hat Enterprise Linux 5.4 was released with support for the Kernel-based Virtual Machine. At this Red Hat event, virtualization -- particularly KVM -- and cloud computing were the most talked about topics. But how is KVM performing these days? With new virtualization refinements going into almost every new Linux kernel release, we have published a new set of KVM benchmarks using the Linux 2.6.31 kernel, to provide updated numbers against our KVM benchmarks from last year and our Core i7 virtualization numbers. This time around, we are also using a Phenom II processor for testing out the AMD-V technology.

I reinstalled Ubuntu with the latest Ubuntu 9.10 yesterday. My virtual machines was much slower than 9.04 when it comes to i/o performance. Something is wrong with the virtualization stack in 9.10. I have now switched back to 9.04.

What bug are you talking about? Are you meaning that is a possible bug?

I think the only way the performance could go *UP* by that much, is that if the virtualization layer isn't properly synchronizing writes or locking or something like that from guest to host, which is almost certainly a serious bug.

The I/O benchmarks are really not representative of a proper KVM setup. I don't know why they published these benchmarks.
Without VirtIO all the network and disk stuff is horrendous, a Google search will tell you that. They really should have used Fedora for this benchmark as well. Ubuntu has always been dodgy in terms of virtualization setups (something is always broken in my experience).Check out the KVM enhancements in Fedora 12! Wow!

I think the only way the performance could go *UP* by that much, is that if the virtualization layer isn't properly synchronizing writes or locking or something like that from guest to host, which is almost certainly a serious bug.

It's not a virtualization bug it's a flaw in the testing.
What's happening is that the host is caching the writes so the data is not being written right away so it would appear to be faster.

Earlier this month at the Red Hat Summit where Red Hat Enterprise Linux 5.4 was released with support for the Kernel-based Virtual Machine. At this Red Hat event, virtualization -- particularly KVM -- and cloud computing were the most talked about topics. But how is KVM performing these days? With new virtualization refinements going into almost every new Linux kernel release, we have published a new set of KVM benchmarks using the Linux 2.6.31 kernel, to provide updated numbers against our KVM benchmarks from last year and our Core i7 virtualization numbers. This time around, we are also using a Phenom II processor for testing out the AMD-V technology.

Testing it on Ubuntu probably won't yield the best results.
You might want to try on RHEL 5.4 where it's been optimized or even on Fedora 11/12

There's lots of optimizations to look at, from setting the IO scheduler to be deadline in the host, to using huge pages, cache settings etc.
Have a look at the video here http://www.redhat.com/promo/summit/2009/highlights/ then click on the "Summit sessions" tab and then virtualization video

What is the outcome of this test?
Software in a VM runs slower - what a suprise ;-)

Wrong, according to the test SQLite ran magnitudes better under VM that native. Most CPU-intensive tasks were just as fast under VM, most hard-disk-intensive tasks were slower under VM. This would imo hint towards a need to develop better virtualization technology for hard disks.